LCDs are commonly used as display devices for compact electronic apparatuses, not only because they provide good quality images with little power consumption but also because they are very thin. The liquid crystal molecules in an LCD do not emit any light themselves. The liquid crystal molecules have to be lit by a light source so as to clearly and sharply display text and images. Thus, a backlight module for an LCD is generally needed.
Referring to FIG. 8, a typical backlight module 10 includes a light guide plate 11, a frame 12, a light source 13, and a reflector film 14. The frame 12 is used for accommodating the light guide plate 11, the light source 13, and the reflector film 14.
The light guide plate 11 includes a light emitting surface 111, a light incident surface 112 perpendicularly connected with the light emitting surface 111, a first side surface 113 perpendicularly connected with both the light incident surface 112 and the light emitting surface 111, and a second side surface 114 opposite to the first side surface 113. A pair of protrusions 115 outwardly extends from the first side surface 113, and another pair of protrusions 115 outwardly extends from the second side surface 114. Any part of each of the protrusions 115 has the same thickness.
The frame 12 includes a first side wall 123 corresponding to the first side surface 113 of the light guide plate 11, a second side wall 124 corresponding to the second side surface 114 of the light guide plate 11, and a third side wall 122 corresponding to the light incident surface 112 of the light guide plate 11. The first side wall 123 has two notches 125 corresponding to the two protrusions 115 of the first side surface 113. The second side wall 124 has two notches 125 corresponding to the two protrusions 115 of the second side surface 114.
The light source 13 includes a plurality of light emitting diodes 131 and a metal strip 130. The plurality of light emitting diodes 131 are adhered on the metal strip 130.
FIG. 9 is an assembled view of the backlight module 10. In assembly, firstly, the light guide plate 11 is put into the frame 12 with the four notches 125 accommodating the four protrusions 115 of the light guide plate 11 respectively. Then the light source 13 is put into a space between the light incident surface 112 of the light guide plate 11 and the third side wall 122 of the frame 12. The light emitting diodes 131 face toward the light incident surface 112.
In practice, the size of the light guide plate 11 does not perfectly accord with the size of the frame 12. Typically, the light guide plate 11 is slightly smaller than corresponding inner dimensions of the frame 12. Thus a gap may exist between the light emitting diodes 131 and the light incident surface 112 of the light guide plate 11. In this circumstance, some of the light beams emitting from the light emitting diodes 131 may not enter the light guide plate 11, and instead leak out from the gap. Therefore, a light utilization efficiency of the backlight module 10 is reduced.
What is needed, therefore, is a light guide plate, a backlight module including the light guide plate, and an LCD including the backlight module, all of which can overcome the above-described deficiencies.